Blinds of these types, which have control filaments, either cords or chains, hanging in loops, have been in use for many years. The slats may be rotated between closed or open positions, and may be raised or lowered, or drawn aside or closed, by the operation of such filaments. Cords or chains of this type are herein referred to as cords as being generic to such filament controls.
It is well known that such cord loops can become tangled and difficult to operate.
In some cases such cord loops have actually been the cause of accidents.
To overcome these problems it has become usual to provide guide blocks for controlling such cords. Such blocks may incorporate a rotatable pulley in some cases, or may simply provide a grooved block around which the cord will slide.
This has to some extent eased the problem of tangling of the cords. However it does not deal with the possible hazards presented by such looped cords.
Another improvement has been the provision of some form of attachment for securing the guide block to the building fabric. Usually this attachment was simply a screw which could be secured to a wall alongside the blind.
When this was done, the cord no longer hung in a free loop. Instead the cord was forced to pass around a fixed path, defined by the guide block secured to the wall. However, it has been found that even when this improvement was provided, this feature of securing the guide block in position, was not always used. For example, where a blind is purchased by a home owner, and installed by him in the home, it was by no means certain that he would follow the directions. As is known many persons do not even read the directions. Consequently in many cases the guide block was simply left unattached.
This could also happen even where the blind was installed by a professional. He might no be familiar with that particular blind. He might fail to insert the screw. Or the screw might pull out.
For all of these reasons it is desirable to provide a blind with a guide block for the cord loop, which guide block has an automatic cord locking mechanism built in, so that if the guide block is loose for any reason, the blind will jam.